The background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
A constant voltage driver for a light emitting diode (LED) is generally more energy-efficient compared to a constant current driver, when implemented using a traditional DC-DC converter. For example, a typical white light LED with a forward voltage of 3.0 V run using 12 mA of current might provide a constant voltage driver of 3.3 V to the LED. The constant voltage driver may include a small 25Ω sense resistor (R=V/I; 0.3 V/0.012 A) in series with the LED, which uses about 3.6 mW (e.g., P=IV; 0.012 A×0.3 V). In comparison, a constant current driver would require 1.2 V instead of 0.3 V at the sense resistor. For 12 mA of current to pass to the LED using a constant current driver, a series resistor of 100Ω (R=V/I; 1.2 V/0.012 A) would be required. Unfortunately, such circuit typically dissipates approximately 14-15 mW in the resistor (e.g., P=I2R; 0.0122 A×100 Ω=14.4 mW). The resistor in both cases (i.e., constant current driver and constant voltage driver) is entirely parasitic and used purely to control the amount of current flowing to the LED to cause the LED to produce consistent lighting.
Such energy waste can be measured by comparing resistor power dissipation to LED power dissipation. For example, a LED in these examples would likely dissipate approximately 36 mW (e.g., P=IV; 0.012 A×3.0 V). In contrast, the resistor in a constant current driven circuit would likely dissipates about 14 mW, while the resistor in a constant voltage driven circuit would likely dissipates about 1.4 mW. Thus, the sense resistor in the constant current LED driver circuit wastes about 28% of the total power dissipated by the circuit, and the sense resistor in the constant voltage LED driver circuit wastes about 9% of its energy, where waste is calculated by dividing by the power dissipated by the sense resistor by the total power consumed by the circuit (e.g., power dissipated by the LED plus power dissipated by the sense resistor).
But a serious issue with the more efficient constant voltage version is that part-to-part variations in the LED forward voltage required to illuminate the component can result in large changes in the LED current. Also, the voltage is affected by environments surrounding the LED. For example, temperature changes can affect voltage drop with similar negative results. A 0.1 V variation in the LED forward voltage could either double the LED current in a particular circuit or even decrease the current to 50% of its expected value, resulting in a dimly lit LED.
Although a slightly higher resistance sense resistor can be used with the LED can so that part-to-part variations will be less sensitive to the LED current. However, increasing the resistance of the sense resistor can lead to additional power waste reducing the power efficiency of the circuit.
Thus, there is still a need for improved methods and systems for reducing energy consumption and requirements of an electric light.